Endless bucket dredge with articulated ladder and swell compensator

ABSTRACT

A deep-digging floating dredge having an articulated ladder with two or more sections pivoted together for relative swinging movement in a vertical plane only and a digging bucket line supported by the ladder. The dredge ladder may have a fixed uppermost section, with either the same or a different bucket line. For sea-going use the dredge may have sounding means for determining instantaneously the height of the hull above the bottom of the water on which the hull is floating, angle sensing means for determining instantaneously the angle to the horizontal of the upper movable ladder section, and control means receiving an input depth signal and an input angle signal controlling the suspension length of the articulated ladder sections and accommodating it to swells in the water level on which the hull floats.

Elite Sttes atnt [191 1 May 22, 1973 Mcay et a1.

[54] ENDLESS BUCKET DREDGE WITH ARTICULATED LADDER AND SWELL COMPENSATOR [76] Inventors: Cameron Edward McKay, 1632 Coronado Way, Burlingame, Calif. 94010; George Paton Barker, Belmar, 85 Sauchenbush Road, Kirkcaldy, Fife, Scotland [22] Filed: Apr. 27, 1970 [21] Appl. No.1 31,945

[51] Int. Cl ..E02f 3/14, E02f 3/16, E02f 7/06 [58] Field of Search ..37/72, 58, 60, 69,

[56] References Cited UNITED STATES PATENTS 3,579,872 5/1971 Jantzen ..37/72 X 246,362 8/1881 Angell ..37/69 2,620,575 12/1952 Pace .37/83 X 3,057,484 10/1962 Trevisan I ..212/58 X 288,091 11/1883 Menge ..37/69 1,762,794 6/1930 Perry ....37/69 3,146,537 9/1964 Von Bolhar ..37/69 1,739,326 12/1929 Posselt ..37/69 UX 1,154,545 9/1915 Penedo ..37/69 3,512,281 5/1970 I-ladjidakis 37/72 X 318,859 5/1885 Bowers ..37/72 UX Primary Examiner-Robert E. Pulfrey Assistant Examiner-Clifford D. Crowder Attorney-Owen, Wickersham & Erickson [57] ABSTRACT A deep-digging floating dredge having an articulated ladder with two or more sections pivoted together for relative swinging movement in a vertical plane only and a digging bucket line supported by the ladder. The dredge ladder may have a fixed uppermost section, with either the same or a different bucket line. For sea-going use the dredge may have sounding means for determining instantaneously the height of the hull above the bottom of the water on which the hull is floating, angle sensing means for determining instantaneously the angle to the horizontal of the upper movable ladder section, and control means receiving an input depth signal and an input angle signal controlling the suspension length of the articulated ladder sections and accommodating it to swells in the water level on which the hull floats.

30 Claims, 27 Drawing Figures PATENTELH:.Y22 I975 SHEET 1 F 12 INVENTORS CAMERON E. Mc KAY BY GEORGE P. BARKER ATTORNEYS PATENTED HAY 2 21973 SHEET 03 m 12 FIG...

ANGLE INDICATOR INVENTOR.

0 CAMERON E. McKAY A7 Y GEORGE R BARKER ATTORNEYS PATENIELIUY22I9I5 SHEET 06 [1F 12 CURRENT SwELL a PITCH D I 83'? SOURCE f423 CORRECTION MODULE 422 vOLTAGE L CURRENT To MULT CURRENT I com 402 42I CURRENT CURRENT 426 COMM SOURCE MULT. T SIGNAL POT 425 L 4 2 3O 3 C 03 vOLTAGE CURRENT/ TO SUM CURRENT AMP MULT' m CONv. E 43I 4OI SU CURRENT AMP MULT. E 403 [434 SIGNAL 433 CHAR.

SIGNAL CURRENT CHAR. MULT. COMM l POT 435 437* C25 VOITISGE CURRENT SU SIGNAL CURRENT REPEATER AMP CHA CONv. 436- 4'5 4IG 4 6 CURRENT SIGNAL O5 REPEATER :2Hg CHAR. I

44 404, 4l7 2 7 CURRENT SIGNAL REPEATER CHAR- 4A3 COMM "Y" C ORDINAT COMMAND MODUL L 440 POT 437 VOLTAGE To ,40s 4O9\ CURRENT CONv.

INvENToRs CAMERON E. MCKAY I 407 "x COORDIN TE COMMAND MOD L GEORGE P. BARKER BY 00m G/QLEKJQE L ATTORNEYS PAH-INTEL II'IY 2 2 I975 SIIEEI D7 III .12

470\ 47l POT 473 44| MOTOR sET POINT 476 OPERATED 2 AUTO-MANUAL J SETTER STATION Sol 503 506 POT 442 MOTOR [502 sET POINT I OPERATED AUTO-MANUAL sETTER STATION 443 MOTOR 2 sET POINT 526 OPERATED AUTO-MANUAL sETTER STATION 440 MOTOR 2?; SET POINT 45s OPERATED AUTO-MANUAL SETTER STATION I 453 454 INVENTORS CAMERON E. McKAY v BY GEORGE P. BARKER ATTORNEYS PATEfiITEL 3,734,564

sum 08 UP 12 INVENTOR,

CAM N E. McKAY,

BY GEO R BARKER ATTORNEYS PATENTEB 1W2 2 I975 SHEEI GS UF I2 47 R 4 SOLENOID '60 6 POSITION I. U U VALVE ADJUSTER I 483 "485 -4S4 MOTOR A870 480 474 8 j VOLTAGE EQL L S J FORWARD LADDER T0 Q SUSPENSION 475 CURRENT -4SI C N ROL IVIODULE CONVERTER MSIS POSITION L I I S gID \46' ADJUSTER f V 5I6 V j: J. MOTOR -I87D 5|O n 504 VOLTAGE To I C07) FEgpQgQCK SUMNIING CURRENT AMPLIFIER CONVERTER INTERMEDIATE IS C7 ggg i LADDER SUSPENSION CURRENT 500*1 CONTROL MOD LE CONVERT R 5l2 POSITION L I MQTQR ADJUSTER U 1 530 /524 VOLTAGE 1 FEEDBACK d, AFTER LADDER T NT (25 Pm SUSPENSION 525 COMES-FER SSI CO TROL MO ULE i POSITION L SOLENOID ADJUSTER v VALVE ll 466 a -l87 460 I MOTOR 454 VOLTAGE T FEEDBACK CUQQENT CZ) POT 57331?? CONVERTER VOLTAGE FEEDBACK I TO (Z POT HEADLINE 464/ CURRENT CONTROL NIODULE CONVERTER PATENTE M 2 21915 SHEET 10 [1F 1 INVENTORS CAMERON E, MCKAY GEORGE P. BARKER ATTORNEYS mgmggumzms ,554

sum 11 0F 12 N EN TOR.

CAMERON McKAY BY GEORGE P. BARKER 0% M ATTORNEYS mgmwwzz ms 3, 554

sum 12 0F 12- NVENTO CAMERON E. MCKAY GEORGE P. BARKER AT OR NEYS ENDLESS BUCKET DREDGE WITH ARTICULATED LADDER AND SWELL COMPENSATOR This invention relates to improvements in floating, deep-digging ladder-type dredges.

BACKGROUND OF THE INVENTION While dredges have been used for many years in gold mining and other similar mining operations, they have heretofore been confined to relatively shallow depths and to relatively quiet waters. Depths up to about 60 to 80 feet have long been dredged successfully, but beyond a depth of about ninety feet below water level, the unit cost of dredging has increased sharply, and such deep-water dredging has become much less economical. As one goes still deeper the costs increase disproportionately.

Thus, although a few dredges have been operated as deeply as about 125 feet below water level, they have not been operated much below that depth for several reasons. For one thing, the manufacturing cost for dredges of prior-art designs capable of digging below about 125 feet below water level was in itself so high as to make the venture uneconomical. Very heavy high-strength ladder girders had to be provided if the large-magnitude live and dead load forces 'were to be withstood. Structures that were efficient for depths of 75 to one hundred feet would not be adequate or efficient at depths of 125 feet and greater. When the dredges were made according to prior-art designs, every additional foot added costs and inefficiencies. Similarly, operating costs of such prior-art structures were also intolerable.

Dredges have encountered problems other than those of depth alone. For example, in operations where the water is not a quiet pond, particularly with offshore dredges operating in the ocean, swells and waves cannot be avoided. The result has been that dredges could operate offshore only during times when the water was very quiet, and they had to remain idle much of the time. Even then, each time a swell or wave would rise, the digging buckets would be lifted from engagement with the sand, soil or rock, and so a large proportion of the time the buckets would come up empty or with only a small proportion of their capacity filled; the alternative to this would have damaged the buckets, the ladder, and related structural and mechanical components by having the buckets repeatedly strike the material being dug with great force as each wave or swell subsided. These same conditions restricted the offshore operations to relatively shallow protected waters, even though it was often well known that in many instances really valuable minerals lay more than a hundred feet below the surface of the ocean in exposed waters which might be fairly close to shore.

SUMMARY OF THE INVENTION The present invention provides a novel articulated ladder structure and other significant structural features in a combination which make deep digging down to two hundred feet and more belowv water level quite practical and economical. The large crosssectional ladder girder thicknesses and the excessive weights that would be required by prior-art structures are avoided and made unnecessary for using articulated structures; thus, the ladders of this invention are provided in a plurality of sections, two or three usually being sufficient, depending upon the total depth needed. By combining these plural sections with adequate rigging lines and maneuvering lines, the depth can be extended at costs that are far less than what one familiar with prior-art structures would have expected. The invention becomes quite significant in locations where it is known that there are extensive deposits of precious metals, gems, commercial minerals, sand, or gravel, or any other subaqueous deposits of commercial value, at depths too great to be accessible at economic costs to the prior-art dredges. The invention is also applicable to dredges utilized for marine construction in excavating both offshore and inland waters.

In the present invention, not only can greater depths be attained, as indicated earlier, but in offshore dredges compensation can be made so that the digging engagement of the dredge buckets, well below the surface, is substantially unaffected by swell and wave conditions. This does not mean, of course, that dredging should be carried on when the seas become rough, but in other than rough or stormy conditions, an ocean-going dredge of this invention can operate efficiently even with relatively high swells and even where the minerals lie well below the surface of the sea. The invention provides a compensating mechanism which is sensitive to swells and waves and which acts to change the angle of the dredge ladder and its approach sufficiently to keep the digging buckets in engagement with the material being dredged.

In connection with these major features of the invention the employment of articulated dredges to get greater depth and the swell-compensating mechanism to enable operation in offshore waters the invention includes a number of other significant features. As noted below, these features materially improve the performance and the economics of the dredges of this invention and give improved performance with lower overall costs.

Insofar as the invention relates to offshore dredging, it applies not only to bucket line dredges, but to any kind of floating ladder dredge; insofar as it relates to deep dredging other than offshore dredging, that is, where the dredge operates in a pond or river where the water level changes very slowly, the invention is particularly directed to bucket-type dredges.

Other objects and advantages of the invention will appear from the following description of some preferred forms thereof.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a simplified view in side elevation of a deepwater dredge, for use in relatively quiet waters, embodying the principles of the invention and having an articulated ladder in two sections.

FIG. 2 is a view similar to FIG. 1 of a modified form of dredge for use in relatively quiet waters in which the ladder is made in three articulated sections.

FIG. 3 is a view similar to FIG. 2 of an offshore dredge embodying the principles of the invention, made in three articulated sections, with an additional fixed ladder section at the top, above the uppermost of the three movable ladder sections. In this view the four ladder sections are all aligned in a straight line.

FIG. 4 is a view similar to FIG. 3 of the dredge of FIG. 3 in a position where the two lower sections are inclined downwardly relative to the upper two sections, in order to compensate for a swell.

FIG. 5 is a view similar to FIG. 3 of an offshore dredge having two movable sections with a fixed ladder section thereabove. The view shows the movable ladder portions in two different positions, the lower position being shown in solid lines and the upper one in broken lines.

FIG. 6 is a diagrammatic view illustrating four different positions of the dredge ladder of FIG. 5, all with the two movable ladder sections kept in a straight line.

FIG. 7 is a view similar to FIG. 5, with the dredge of FIG. 5 shown with the lower movable ladder section inclined downwardly from the upper movable ladder section to compensate for a swell. An upper position of the lower movable ladder section is shown in broken lines.

FIG. 8 is a diagrammatic view illustrating four different positions where the angle between the two ladder sections remains as in FIG. 7.

FIG. 9 is a block diagram of control apparatus for obtaining compensation for swell through the ladder suspensions and headline in the dredge of FIGS. 3 and 4.

FIG. 10 is a diagrammatic view in elevation of the input system for the compensation apparatus of FIG. 9.

FIG. 11 is a diagrammatic view in elevation of the ladder-suspension control apparatus of FIG. 9.

FIG. 12 is a diagrammatic view in elevation of a headline compensating apparatus used in the control of FIG. 9.

FIGS. 13A, 13B and 13C comprise an electrical circuit diagram for the device of FIG. 9 to 12.

FIG. 14 is a view in side elevation of a modified form of dredge having two movable ladder sections and a secondary fixed-position ladder to which the upper of the two movable sections transfers the bucket load.

FIG. 15 is an enlarged view of the fixed ladder ramp and the upper portion of the articulated pivoted ladder sections, broken twice in the middle and at each end of the frame, also showing the upper tumbler and its drive machinery, the upper pivoted connection of the swingable ladder, and the intermediate pivoted connection for the articulated ladder sections.

FIG. 16 is a similar view of the same parts in side elevation.

FIG. 17 is a view similar to FIG. 15 of the lower portion of the articulated ladder, broken in the middle of the framework, also showing an optional form of combined ladder end and an optional form of bucket idler located at the pivotal connection of the articulated ladder sections.

FIG. 18 is a view similar to FIG. 17, showing the same parts in side elevation.

FIG. 19 is a view in section taken along the line l9-l9 in FIG. 16, showing the independent structural supports for both the fixed upper ladder ramp and the upper pivoted connection of the swingable ladder.

FIG. 20 is an enlarged fragmentary view in side elevation of the upper part of the fixed ramp ladder generally like that of FIG. 15, but with a modification incorporating, in addition to the main discharge chute, a series of save-all grizzly bars and a save-all collection chute.

FIG. 21 is a fragmentary top plan view of a dredge having a skew suspension for its lowermost articulated ladder section.

FIG. 22 is a similar view in side elevation.

FIG. 23 is a detailed fragmentary view of the connection of the suspension to the lowermost ladder section.

FIG. 24 is a fragmentary view in side elevation enlarged with respect to FIG. 22.

FIG. 25 is a view similar to FIG. 5 of a dredge having a fixed upper ramp and a single swingable ladder section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dredge of FIG. 1, which is designed for deep dredging in relatively quiet waters, such as a pond, a sheltered bay, or a river where the water level changes rather slowly, has a hull 51 with superstructure 52. The hull 51 and the superstructure 52 support the uppermost of two articulated ladder sections 53 and 54 by means ofa pivot axis member 55 at the top of the upper ladder section 53, which may also provide the axis of rotation of an upper tumbler 56. The lower ladder section 54 is attached to the lower end of the upper ladder section 53 by a pivot member 57, and it carries a lower tumbler 58 at its lower end. A single continuous bucket line 60 goes around the two ladder sections 53 and 54, passing from a turnover at the upper tumbler 56 down to the digging position at the lower tumbler 58. On their upper run the buckets 61 ride across supporting planar ladder surfaces 62 and 63, and on the lower run their slack may be taken up somewhat by one or more intermediate idlers; shown is an underrun bucket idler 64 on the hull 51 and an underrun bucket idler 65 supported from the upper ladder section 53. These idlers 64 and 65 help to limit slack and tension in the bucket line, among other things.

The underrun bucket idler 65 can be located within or very close to the suspension points of the adjacent ladder section 53, thereby minimizing the bending moment in that ladder section 53, which is induced by the weight of the underrun buckets 61 carried by the idler 65. This structure is not possible in conventional onepiece ladders, where the bucket idlers must be located approximately midway between the upper and lower ends of the one-piece ladder, thereby inducing the maximum bending moment. The idler 65, when located according to the present invention, contributes further to enabling reduction in the required section-size and weight of all of the swingable ladder sections. Alternately, conventional caterpillar-type idlers may be used in lieu of the wheeltype idlers 65 shown, with the same location advantages.

Each of the articulated ladder sections 53, 54 is adapted to swing pivotally relative to the hull 51 and to its adjacent ladder section. The support and relative swinging may be accomplished by means of a forward ladder suspension 66 and an after ladder suspension system 67, each of which comprises a block-and-tackle assembly and a plurality of cables 68 secured to its ladder. A headline 70 at the forward end of the hull 51 passes over a pulley 71 down to a headline winch 72, and each of the ladder hoists includes a cable 73 or 74 passing from an upper pulley of the suspension system 66 or 67 to a winch 75 or 76, located at appropriate locations on the hull 51. The forward ladder suspension system 66 is, of course, the longer, since the forward ladder 54 goes down deeper.

At the upper end of the after ladder 53, adjacent the upper tumbler 55, there may be a revolving screen 77 which receives the material that is dumped from the buckets 61 through an open end 78 and slopes down over a tail sluice 80. The oversized dredged barren material goes through the screen 77 and into the tail sluice 80, with the valuable mineral-containing fraction going through the screen perforations and out to the side in a part not shown in FIG. 1 but well known in dredges. At the tail sluice 80, the dredged mineral-barren material washes back in a well-known manner, the tailings going out the end of the tail sluice 80 and gradually building up there. Other conventional apparatus for handling the dredged material for mineral recovery or for other purposes may be employed, many such being well known in the dredge art.

In order to enable the ladders S3 and 54 to move up and down from below the hull to above it and back, a suitable well-side slot 81 is provided on the hull 51 to receive the pivot assembly 57 between the ladder sections 53 and 54.

By making the ladder articulated, neither of the ladder sections 53 and 54 has itself to withstand all of the burden; so each ladder section 53 and 54 can be substantially smaller in cross-section and in weight than a one-piece ladder properly designed to do the job. A single ladder capable of dredging down to the depths contemplated in this invention would have to be very heavy and very thick, and it therefore would be quite difficult to raise and lower, as well as being expensive to construct. But by having the ladder in more than one section with an articulated joint between sections and with two suspension assemblies, a much more efficient operation is obtained, enabling far greater depth without correspondingly larger structures.

Broken lines 82 and 83 in FIG. 1 show, respectively, (1) how the two ladder sections 53 and 54 can be dropped lower and in line and (2) how the lower ladder section 54 can be used at a different angle in line with the upper ladder section 53. In the solid line position, the lower ladder section 54 is dropped below the centerline continuation of the upper ladder 53.

FIG. 2 shows a similar dredge 100 with a hull 101 and having a three-section ladder assembly with an upper ladder section 102, an intermediate ladder section 103 and a lower ladder section 104. The dredge 100 is capable of being used at depths even greater than those of which the FIG. 1 device is capable. It is feasible to go beyond FIG. 2 and have more than three movable articulated ladder sections. Once again, the general principle is the same. The upper ladder section 102, while movable, does not necessarily have to move during times when both the intermediate ladder section 103 and the lower ladder section 104 swing, and the lower ladder section 104 can be swung relative to the intermediate ladder section 103, the broken lines 105, 106, and 107, illustrating some of the ladder positions.

Each ladder section 102, 103, and 104 has its suspension 112, 113, or 114, like the suspensions 66 and 67. The bucket line 110 is like the bucket line 60, but longer. There are two well-side slots 115 and 116 to accommodate the two pivot members 117 and 118. Each suspension 112, 113, 114 has its winch 122, 123, and 124. The headline 120, the rotating screen 121, and tail sluice 125 are like the corresponding parts in FIG. 1, and the upper tumbler 126 may rotate about the same axis as that for the pivot for the upper ladder section 102. Operation is basically the same as for the dredge 50.

FIGS. 3 to 13 relate to offshore dredging, where the problems brought on by waves and swells are met. In

addition there are some other structural differences which are applicable to quiet-water dredges.

FIGS. 3 and 4 show an offshore dredge 130 generally similar to the dredge 50 of FIG. 2, but having some important differences. The hull 131 and superstructure 132 support an articulated ladder having three swingable sections 133, 134, and 135, pivoted to each other at pivots 136 and 137, while the after ladder 133 is pivoted to the superstructure by a pivot 138.

In addition, however, this dredge 130 provides a fixed ladder section or ramp 140 above the after ladder 133. The bucket line 141 continues up the ramp 140 and around an upper tumbler 142 there. This ramp or fixed ladder section 140 is never moved and enables the attainment of a higher upper level without having to increase the section thicknesses and weight of the uppermost movable ladder section 133. As a result, of course, greater depths can be obtained with substantially the same movable ladder sections as in FIG. 2, since the fixed ladder section 140 takes up a substantial portion of the total ladder length involved.

The broken line 155 shows how the three ladder sections 133, 134, and 135 may be kept in line while being swung relative to the fixed ladder section 140. During this swinging, the position of the upper portion of the bucket line 141 is not changed, and it still is able to dump its load into a rotating screen 156 (or other receiving apparatus) with the relationship between the bucket line 141 and the screen 156 (or other receiving apparatus) remaining unchanged. The underrun bucket line 141 goes down to a lower tumbler 143, via idlers 144 and 145. The idler 145 has the advantage, previously noted as to the idler 65 of FIG. 1, of minimizing the bending moment of the ladder section 133, by being located within or close to its suspension point. Suspensions 146, 147, and 148 are operated by respective winches 150, 151, and 152 to raise and lower each ladder section 133, 134, and 135, either all together, or separately.

The other principal differences which distinguish the FIG. 3 structure from that of FIG. 2 are those that enable the dredge of FIG. 3 to be used in offshore or ocean waters where there are swells, so that difference between the crests and troughs may be up to twenty feet or even more. It is apparent that if no attempt is made to compensate for the swelling, the dredge buckets will either come up empty most of the time or will crash into the solid bottom some of the time. In the present invention, the dredging face is kept substantially constant, to maintain uniform and continuous digging production and to eliminate cyclical impact forces to the lower ladder end where the digging mechanism is located. The lower tumbler 143 is kept in a fixed position for any selected digging depth, in relation to the dredging face and the dredged sea bottom 153 irrespective of the water surface conditions in terms of waves and swells. The lower tumbler 143 remains at its fixed x, y position (or the x, y position shown in broken lines) for any selected digging depth, while the ladder 133, 134, 135 traverses the lower tumbler 143 lat erally from port to starboard or starboard to port in the process of excavating the subaqueous material. The compensating mechanism includes (1) a sounding device 154 suspended by a cable 157 and (2) an angle indicated 158, which are shown in FIG. 3 and, in more detail, in FIG. 10.

FIGS. 3 and 4 illustrate the broad effect of the compensating mechanism, which is shown in more detail in FIGS. 9-13. FIG. 4 shows the dredge 130 as it is at a swell crest, and FIG. 3 shows the same dredge 130 in the swell trough. During the trough time the dredge hull 131 is closer to the bottom 153 than during the crest time; therefore during the crest the two lower ladder sections 134 and 135 are dropped to gain additional depth, as shown in FIG. 4, the upper section 133 here remaining unchanged. However, only the lower ladder section 135 may be dropped for swells of lesser magnitude. As the water level drops again to the trough, the ladder is straightened out and may return to the common center line shown in FIG. 3.

FIGS. 5-8 help to clarify the general aspect of this compensating action while also illustrating an alternative dredge 170 having a hull 171, superstructure 172, a fixed upper ramp or ladder 173 and two swingable ladder sections 174 and 175 with their suspensions 176 and 177 and articulated joint or pivot 178 and an upper pivot 179 for the section 174.

The use of the fixed upper ramp 140 (FIG. 3), 173 (FIG. 5), or 323 (FIG. 25) in the invention enables either l) a shorter length of suspended ladder 133, 134, 135 (FIG. 3) or 174, 175, (FIG. 5), or 324 (FIG. 25), with the ensuing advantages of having less suspended ladder weight, less required capacity in the ladder suspension and hoisting systems and a reduction in the structural requirements of certain elements of the superstructure, or (2) increasing the digging depth of existing conventional dredges by installing a fixed upper ladder ramp 140 or 173 or 323 and then utilizing an original suspended ladder 324 with its upper pivot connection relocated at a lower position, whether or not additional pivoted ladder sections 174 or 134 and 135 are added thereto.

FIG. 5 shows, in broken lines, an upper nearly horizontal stowed position of the ladder sections 174 and 175. In solid lines it shows a lower digging position also with the ladder sections 174 and 175 in a straight line. FIG. 6 shows, in diagrammatic form only, four positions A, B, C, and D of the ladder combination 174, 175, always kept in a straight line for trough conditions. These four positions correspond to different stages of digging when the dredge makes its bite at different levels along a digging face.

FIGS. 7 and 8 correspond to swell crest conditions of the dredge 170, with the lower ladder section 175 inclined downwardly about its pivot 178, by slacking its suspension 177. Positions A, B, C, and D in FIG. 8 are the same as the same positions in FIG. 6, with the ladder section 175 inclined to make up for the rise in level of the hull 171. The idea, thus, is to compensate for the difference in vertical distance of the hull 171 above the bottom 153 by so dropping the lower ladder section 175 relative to the ladder section 174 that the lower tumbler 180 remains in exactly the same position as the water rises and falls.

As shown in FIG. 10, the sounding device 154 of well-known type acts through a cable 157, e.g., in cooperation with pulleys 149 and a weight 159, to provide a mechanical signal indicating the change in the vertical position ofthe dredge hull 131 up and down as crest and trough conditions occur. This may be interpreted as the height of the hull 131 above the bottom 153 or may be taken from any predetermined point of reference. The mechanical signal from the sounding device 154 is used mechanically to vary the resistance setting of a swell potentiometer 401. Similarly, the angle indicator 158 is set at or adjacent the pivot member 138 and acts mechanically to vary the resistance setting of a pitch potentiometer 402, in accordance with the angle which the true horizontal makes with the nominally horizontal center line of the hull 131. The potentiometers 401 and 402 transmit electrical signals as voltages to a swell-and-pitch correction module 403, as shown in FIGS. 9 and 13A. The swell-and-pitch correction module 403 operates in cooperation with a Y- coordinate command module 404 having a command potentiometer 405 and an X-coordiante command module 406 having a command potentiometer 407. The modules 403, 404, and 406 are described below and are illustrated in FIG. 13A.

The lower tumbler 143 is initially positioned into a preselected x, y (or x, y) position by the Y-coordinate command module 404 and the X-coordinate command module 406; these command modules 404 and 406 may be command by a winchman manually through the potentiometers 405 and 407 For a dredge like that of FIGS. 3 and 4, the Y-coordinate command module 404 provides three signals Y1, Y2, and Y3, one to set each of the three ladder suspensions 148, 147, and 146, respectively, to move its ladder section 135, 134, and 133 to the proper elevation. In a dredge like that of FIGS. 5-8, there are only two such signals because there are only two ladder suspensions 176 and 177. In both types of dredge there is only one signal from the X-coordinate command module 406 because that signal controls only the headline 184.

As the dredge hull 131 begins to rise vertically on an incoming swell from the FIG. 3 position to the FIG. 4 position, the conventional automatic sounding device 154 indicates the depth of water between the dredged bottom datum 153 and the dredge hull 131. This depth is transmitted by the cable 157 and the swell potentiometer 401 to the swell-and-pitch correction module 403 (FIG. 9) to provide correction signals 435, 436, and 437 respectively for the Y1, Y2, and X coordinates. A forward ladder suspension control module 470 and an intermediate ladder suspension control module 500 receive respective corrected signals 441 and 442 and issue a command signal causing respective hydraulic-system solenoid valves 160 and 161 to open (see FIG. 11) so that respective pistons 162 and 163 in hydraulic cylinders 162a and 163a move to the left, and respective sheaves 164, 165 moves from position D towards position C, thus paying out lufflines 168 and 167 to the forward and intermediate ladder suspensions 148 and 147 respectively by an amount such that the lower tumbler 143 remains at its desired digging elevation, the y coordinate. Meanwhile, a headline control module 450 (FIG. 9) receives a corrected signal 440 and issues a command signal for a hydraulic-system solenoid valve 181 to open (See FIG. 12), moving a piston 182 in a cylinder 182a to the right, and a sheave 183 moves from position E toward position F, thus taking up on a headline 184, so that the lower tumbler 143 remains at its x digging coordinate. Thus, the x, y position of the lower tumbler 143 remains the same.

On a falling swell the sounding device 154, the transmitting swell potentiometer 401, and swell-and-pitch correction module 403 provide signals for reverse action of the compensating system, that is, the lufflines 9 168 and 167 are taken up and the headline 184 is paid out the required amount.

The forward and intermediate ladder suspension control modules 470 and 500 and the headline control module 450 issue commands for the compensation cylinders 162a and 163a and 182a to adjust for the variable swells. When the vertical rise and fall of the dredge hull 131 under swell condition causes the pistons 182, 162 and 163 to approach the end of their travel in or out, limit switches 185, 186 or 185a, 186a or 185b, 186b, completing the raise or lower circuit to their respective motors 187, 187a, 187b to pay out or take up lines 184, 168 or 167, as the case may be, over the travel capacity of the hydraulic cylinders 182a, 162a, and 163a, until the controller signal is broken. In the case of single headline 184, the practical travel capacity of the system is adequate for a headline travel for a related vertical motion of the dredge hull 131.

The swell signal is corrected by a suitable angle measuring device 158 (FIG. 10), that measures the variable angle 3 between the horizontal center line of the hull 131 and true horizontal, which, in itself, compensates for foreand-aft hull trim under sea conditions, further insuring the desired positioning of the lower tumbler 143 at all times. This angle is transmitted to the swelland-pitch control module 403 by the potentiometer position indication 402.

Of the command modules 403, 404 and 406 (FIGS. 9 and 13A) the X-coordinate command module 406 is the simplest, comprising basically a voltage-to-current converter 408 and a summing amplifier 409, as shown in FIG. 13A.

The voltage-to-current converter 408 and all the other voltage-to-current converters spoken of in this specification, may be off-the-shelf items. For instance, they may each be a Foxboro 666T or 66GC series voltage-to-current converter. These converters accept a l to volt DC input and convert it to a proportional to 50 milliampere DC output. A constant current source forming part of this converter excites a remote slide wire, such as the command potentiometer 407. A thousand-ohm slide wire with travel adjusted to approximately 155 to 825 ohms may provide the one-tofive volt DC signal, which is fed to the input of the converter 408. Other values, of course, can be provided. The converter 408 may contain a magnetic and transistor amplifier and be connected to a supply voltage. Since it is an off-the-shelf item, it need not be further described.

Similarly, the summing amplifier 409 and all the other summing amplifiers used here may be a Foxboro 66CT or 66CC series electronic Consotrol summing amplifier. These summing amplifiers are able to receive up to four 10 to 50 milliampere DC input signals and to provide a 10 to 50 milliampere DC output signal that is proportional to them. The summing amplifier may be a solid-state unit with a two-stage magnetic amplifier connected to a suitable supply voltage. As'will be seen in this invention, some of the summing amplifiers are used with only two input signals, while others are used with more input signals.

The Y-coordinate command module 404 includes a voltage-to-current converter 410 like the converter 408, which takes its input from the command potentiometer 405 and which supplies, in this instance, three current repeaters 411, 412, and 413. These current repeaters, like the others used in this invention may also be off-the-shelf items, such as the Foxboro 663T and 663C series electronic Consotrol current repeaters. These repeaters receive a 10 to 50 milliampere DC input signal and produce an electrically isolated 10 to 50 milliampere DC output. They have a low input resistance of about ohms and can feed an external load up to 660 ohms. Such units are often used to extend the total load fed by computer devices to transmitters. They may be of solid-state construction throughout with a magnetic transistor amplifier, and, of course, they have many uses other than in this invention. Each of them is connected to a suitable supply voltage.

The Y-coordinate command module 404 also includes two summing amplifiers 414 and 415, both connected to the current repeater 412. These summing amplifiers 414 and 415 may be off-the-shelf units identical to the summing amplifier 409 already described. Each of these summing amplifiers 414 and 415 feeds its signal to a signal characterizer 416 or 417, while the current repeater 413 feeds its signal directly to a signal characterizer 418 to produce the Y3 output 443. Each of these signal characterizers 416, 417, and 418, like others to be mentioned later, may be off-the-shelf items. For example the Foxboro 66N series signal characterizer, is a completely solid-state instrument that provides up to eight slope adjustments and up to eight break point adjustments for the generation of both linear and nonlinear functions. It includes a buffer amplifier, a shaping circuit, and an operational amplifier, which can be connected in various ways with other minor ingredients.

The swell-and-pitch correction module 403 has two inputs, as already noted, one from the swell command potentiometer 401 operated by the sounding device 154, which feeds into a voltage-to-current converter 420, and the other from the pitch command potentiometer module 402 operated by the angle generator 158, which feeds its output to another voltage-to-current converter 421.

The voltage-to-current converter 421 feeds its current output to a current multiplier 422, which is supplied by a constant current source 423 and to another current multiplier 424, fed by a constant current source 425, to achieve two different multiplied outputs. These current multipliers may also be off-the-shelf items, such as the Foxoboro 66DT and 66DC series electronic Consotrol multiplier dividers. These are solid-state analog computing instruments which receive up to three DC input signals at 10 to 50 milliamperes and put out a 10 to 50 milliamperes DC output signal which is proportional to the computed value. There is no electrical isolation between the input, so that only one of the input circuits can be grounded and there should be no external common connections between the input circuits. The constant current sources 423, 425 used for these multipliers may each be an off-the-shelf item such as a Foxboro 66ET and 66EC series electronic Consotrol current source, which provides an output that is adjustable from 10 to 50 milliamperes. Each may include a transistorized amplifier and other features. Here they are used only for reliable current sources of a standard current to give a fixed multiplier.

Thus, the current multipliers 422 and 424 are used to supply two independent products originating from the same signal. They may be supplying substantially the same product or they may be supplying a different product, depending on the setting of the current sources 423 and 425.

The swell-and-pitch correction module 403 also includes three signal characterizers 426, 427 and 428 (like the signal characterizers 416, 417, 418). It also includes a pair of summing amplifiers 430 and 431 and three current multipliers 432, 433 and 434. The current repeater 411 of the Y-coordinate command module 404 is connected to the signal characterizer, 426 and 427 of the swell-and-pitch correction module 403. The current multiplier 422 and the voltage to current converter 420 are connected to the summing amplifier 430, and the voltage-to-current converter 420 is also connected to the summing amplifier 431, to which is also connected the output from the current multiplier 424. The output from the summing amplifier 430 is connected to the current multipliers 432 and 433. The signalcharacterizer 426 is also connected to the current multiplier 432, so that the output (or correction signal) 435 from the current multiplier 432 is proportional to the product of the multiplication of the outputs of the signal characterizer 426 and the summing amplifier 430. The summing amplifier 431 and the signal characterizer 427 are connected to a current multiplier 434, whose output or correction signal 436 is proportional to the product of those two inputs.

The current repeater 412 of the Y-coordinate command module 404 is connected to the summing amplifiers 414 and 415, and the current multiplier 434 feeds its output or correction signal 437 to the summing amplifier 415. The output from the summing amplifier 415 goes to the signal characterizer 417, which thereupon produces the Y2 output 442.

The current repeater 412 also feeds its signal to a signal characterizer 428 which feeds its output to the current multiplier 433, and the output from the current multiplier 433 is fed to the summing amplifier 409, which is otherwise fed directly by the voltage-tocurrent converter 408 of the X-command module 406. This produces the signal output 440 of the X-command module 406.

The current multiplier 432 is fed to the summing amplifier 414, as is the signal from the current repeater 412, and the sum of these is then fed to the signal characterizer 416 to produce the Y1 output 441.

What has been described so far, then, results in a single output 440 from the X-command module and three outputs 441, 442, and 443 from the Y-coordinate command module, and this concludes the description of FIG. 13A.

The output 440 from the X-coordinate command module is fed to the X-coordinate control module 450. The output 440 is fed directly to a motor operated setter 451 of the control module 450 (FIG. 138). This, like the other motor operated setters to be described, may also be an off-the-shelf item, such as, the Leeds and Northrup Companys M-line, model C, motor operated setter. This motor operated setter 451 tracks the signal 440 and positions a retransmitting slide wire which is a set point potentiometer 452 for a set pointlauto-manual station 453, the set point potentiometer 452 being fed directly to the set point/auto-manual station 453. This, like the other set point/auto-manual stations to be described, may also be an off-the-shelf item such as the Leeds and Northrup Companys M-line, model C, P.A.T., set point/auto-manual station. The set point/auto-manual station 453 compares the set point potentiometer 452 with the output 454 of a position feedback summing amplifier.455 (see FIG. 13C), and the unbalance between these two signals becomes an error signal 456 that is proportional in magnitude and polarity to the unbalance.

The output 456 is fed directly to a position adjuster 460 (FIG. 13C). This, like the other position adjusters to be described, may also be an off-the-shelf item, such as the Leeds and Northrup Companys P.A.T. control known as the M-line Module C control unit. These are used for electric drive units to provide precise control of process variable. They receive an error signal or input (e.g., the error signal 456 in this instance) from the set point unit 453 (See FIG. 13B) and, through an amplifier, energizes either a raise relay or a lower relay, depending upon the polarity, magnitude, duration and rate of change of the error signal. They are used in closed loop control systems as the heart of the unit. They are complex units but are well known and are completely described in published material. The signal 440 is used here as the set point, and the position feedbacks are set mechanically through positionfeedback potentiometers 461 and 462.

With reference to FIGS. 11, 12, 13B, and 13C, the position-feedback potentiometer 461 feeds its signal to a voltage-to-current converter 463 (like the converter 408), and the position feedback potentiometer 462 feeds its signal to a voltage-to-current converter 464 of the same type. The outputs from the converters 463 and 464 are fed to the summing amplifier 455, which feeds its output 454 into the set point/auto-manual station 453 that provides the error signal 456 to the position adjuster 460. The position adjuster 460 has two output cables 465 and 466, the cable 465 feeding raiselower control power to the solenoid valve and a pump 188a for the compensating system hydraulic cylinder 162a, and the cable 466 feeding raise-lower control power to the motor 187 for the headline winch 189.

The output 441 from the Y-coordinate command module 404 is fed to a control module 470. The output 441 is fed directly to a motor-operated setter 471 (FIG. 138), like the motor-operated setter 451. The motor operated setter 471, tracks the signal 441 and positions a retransmitting slide wire set point potentiometer 472 feeding directly to a set point/auto-manual station 473. The set point/auto-manual station 473 compares the set point potentiometer 472, with the output 474 of a voltage-to-current converter 475, and the unbalance between these two signals becomes an error signal 476 that is proportional in magnitude and polarity to the unbalance. The output or error signal 476 is fed directly to a position adjuster 480. The control module 470 also has a position-feedback potentiometer 481 sending a signal to the voltage-to-current converter 475 which provides the base signal for the position adjuster 480, from which outputs 482 and 483 are fed to the solenoid valve 160 and pump 188a forward ladder hoist motor 187a for the winch 152.

The Y-coordinate command module 404 sends its second or Y2 signal 442 to a control module 500. The output 442 is fed directly to a motor operated setter 501, which tracks the signal 442 and positions a retransmitting slide wire set point potentiometer 502, which is fed directly to a set point/auto-manual station 503. The set point/auto-manual station 503 compares the set point potentiometer 502, with the output 504 of a position feedback summing amplifier 505, and the unbalance between these two signals becomes an error signal 506 that is proportional in magnitude and polarity to the unbalance. The output or error signal 506 is fed directly to a position adjuster 510 like those previously described. The signal 442 is used as the set point signal, and the units position feedback is controlled by two feedback potentiometers 511 and 512 respectively feeding voltage-to current converters 513 and 514, the outputs of which are added by the summing amplifier 505. The outputs 515 and 516 from the position adjuster 510 is then used to control the solenoid valve 161 and hydraulic pump 188b and the intermediate ladder hoist motor 187]; for the winch 151.

The third output signal from the Y-coordinate command module 404 is the signal 443, which is fed to a control module 520. Here again, the output 443 is fed directly to a motor operated setter 521 which tracks the signal 443, and positions a retransmitting slide wire set point potentiometer 522. The set point potentiometer 552, is fed directly to a set point/auto-manual station 523 which compares the set point potentiometer 522, with the output 524 of a voltage-to-current converter 525, and the unbalance between these two signals becomes the error signal 526 that is proportional in magnitude and polarity to the unbalance and is fed directly to a position adjuster 530. The position feedback is set by a feedback potentiometer 531 feeding its signal to the voltage-to-current converter 525. A single output 532 from the position adjuster 530 is connected to the after ladder hoist motor 190 for the winch 150.

As shown in FIGS. 9 and 11, each of the three ladder suspensions shown in FIG. 11 receives feedback from its command potentiometers, each of which is related to the position of the devices controlled thereby. Thus, the control module 470 for the forward ladder 135 receives feedback from its position-indicating potentiometer 481 that is located adjacent a pulley 191 for the suspension line 148. The intermediate control module 500 for the ladder 134 receives feedback from the potentiometer 511 that indicates the position of the traveling sheave 165 and from the potentiometer 512 that indicates the position of the winch drum 151. The control module 520 for the after ladder 133 receives feedback from its potentiometer 531 that indicates the position of the winch drum 150.

Similarly, as shown in FIGS. 9 and 12, the command module 450 for the headline 184 receives feedback from the command potentiometer 461 indicating the position of the traveling sheave 183 and from the potentiometer 462 indicating the position of the winch drum 189.

In operation, the command signal for the Y- coordinate command 'module 404, provided by the potentiometer 405, which is calibrated in feet, is adjusted by the dredge winchman. The slidewire excitation signal built into the voltage-to-current converter 410 provides the excitation for the potentiometer 405, and the output signal of the voltage-to-current converter 410 drives the three current repeaters 411, 412, and 413. The output from the current repeater 411 drives the two signal characterizers 426 and 427 in the swell-andpitch correction module 403. The output from the current repeater 412 drives the two summing amplifiers 414 and 415, and the signal characterizer 428 in the swell-and-pitch correction module 403. The output of the current repeater 413 drives the signal characterizer 418, whose output signal 443 is the Y3 output 443 used to drive the after ladder suspension control module 520.

The two summing amplifiers 414 and 415 provide the sum of Y plus Y1 and Y2. Their output drives the signal characterizers 416 and 417 which respectively provide the Y1 and Y2 output signals 441 and 442 that drive the forward and intermediate ladder suspension control modules 470 and 500 respectively.

The X-coordinate command module 406 input signal is fed to the voltage-to-current converter 408 and from there to the summing amplifier 409, whose other input signal comes from the swell-and-pitch correction module 403, and the output 440 therefrom drives the headline control module 450.

The swell-and-pitch correction module 403 receives four signals; first and second are from the respective current repeaters 411 and 412 of the Y-coordinate command module 404; third, the pitch from the potentiometer 402 that is positioned by the angle indicator 158; and fourth, the swell from the potentiometer 401 which is positioned by the sounding device 154. The pitch signal is proportional to the tangent of angle B, and is sent to the two multiplier amplifiers 422 and 424. The second input to each of the multiplier amplifiers 422 and 424 is the constant signal provided respectively, by the two current sources 423 and 425 which represent one leg of a triangle. The outputs of the two multiplier amplifiers 422 and 424 are equal to the Y1 and Y2 pitch component, and these two components are inputs to their respective summing amplifiers 430 and 431.

The swell signal from the voltage-to-current converter 420 is proportional to the vertical distance that the bottom of the dredge hull 131 lies above the trough of the swell, and this signal is the other input to the two summing amplifiers 430 and 431. The output of the summing amplifiers 430 and 431 are the values of the swell pitch components Y1 and Y2. The swell pitch components, outputs of the summing amplifiers 430 and 431 are corrected according to the depth the dredge is digging by the multiplier amplifiers 432 and 434, whose second inputs are from the signal characterizers 426 and 427 which are driven by a Y coordinate signal. The outputs 435 and 436 of the multiplier amplifiers 432 and 434 are then equal to the required Y1 and Y2 coordinate correction, which are inputs to the Y-coordinate command module 404.

The X coordinate is computed by the Y1 output from the summing amplifier 430 as one input to multiplier amplifier 433, and the second input is the output from the signal characterizer 428, which is driven by a Y coordinate signal. The output 437 of X coordinate multiplier amplifier 433 is the correction input to the X-coordinate command module 406.

The swell and pitch signal may be adjusted and calibrated so that the final output signals 440, 441, 442, and 443 are all positive.

The set point of the position adjuster 480 is adjusted by the input signal 441 from the Y-coordinate command module 404. This set point signal 441 is balanced against the actual feedback signal 474 from the potentiometer 481 and the voltage to current converter 475, which represent the actual Y-coordinate of the lower tumbler 143. The resultant error signal 476, proportional to the deviation and direction of the lower tumbler 143 from the set point, is transmitted to the posi- 

1. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising a plurality of sections pivoted together for relative swinging movement in a vertical plane only and including an upper tumbler at the top of the ladder, an upper swingable ladder section having a main pivot adjacent its upper end supported by said superstructure, and a lower swingable ladder section having a clevised upper end with clevis arms supporting a shaft and pivoted thereby to the section above it at a lower end lying between the clevis arms, said lower ladder section having a lower tumbler at its lower extremity. a bucket-line guide roller supported by said shaft and thereby at the pivot line of the upper and lower swingable sections, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and meeting and leaving said bucket-line guide roller tangent thereto and supported by said ladder, said bucket-line guide roller and clevis structure enabling maximum downward swinging of said lower section relative to said upper section while maintaining the bucket line in proper alignment with said ladder, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull.
 2. The dredge of claim 1 wherein there are at least three swingable sections successively pivoted to each other For relative swinging movement in a vertical plane only as well as being pivoted to said superstructure at the upper end of the upper section thereof, each pivoted connection having a clevis connection as recited with a bucket-line guide roller sup-ported on the pivot line thereof.
 3. The dredge of claim 1 wherein the lower end of said swingable lower ladder section is suspended by two sets of block-and-tackle suspensions lying in the same plane but inclined to each other set at acute angles symmetrical about the center line of the dredge and of the multiple section ladder.
 4. A floating deep-digging dredge, including in combination: a hull, superstructure supported on said hull, an articulated ladder comprising a plurality of sections pivoted together for relative swinging movement in a vertical plane only and including an upper driving tumbler supported by said superstructure near the top of the ladder, an upper swingable ladder section having a main pivot adjacent its upper end supported by said superstructure, at a point below and near said upper tumbler a lower swingable ladder section pivoted to the section above it and having a lower tumbler at its lower extremity, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull.
 5. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising a plurality of sections pivoted together for relative swinging movement in a vertical plane only and including an upper tumbler at the top of the ladder, an upper swingable ladder section having a main pivot adjacent its upper end supported by said superstructure, and a lower swingable ladder section pivoted to the section above it and having a lower tumbler at its lower extremity, said ladder having a fixed uppermost section, supported by said superstructure, said superstructure also supporting said upper tumbler, said upper swingable ladder section being pivoted on said superstructure below and independent from said fixed uppermost section, for swinging movement relative to said fixed section, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull.
 6. The dredge of claim 5 wherein said fixed uppermost ladder section is located and arranged to provide at all times a constant tangent alignment of the bucket line leading to the pitch circle of the upper tumbler and coaxial with a shaft which supports the upper tumbler.
 7. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising two swingable ladder sections pivoted to each other for relative swinging movement in a vertical plane only and including an upper driving tumbler supported by the superstructure near and separate from the top of the ladder, the upper ladder section being pivoted at its upper end directly to said superstructure independently of the upper driving tumbler, and a lower swingable ladder section pivoted to said upper ladder section and having a lower tumbler at its lower extremity, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, a plurality of block-and-tackle suspensions supported bY said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull.
 8. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising a fixed uppermost ladder section and at least one swingable ladder section pivoted at its upper end to said superstructure at an uppermost pivot for swinging movement relative to said fixed section in a vertical plane only, said uppermost pivot being supported independently of said fixed ladder section, an upper tumbler at the top of said ladder, a lower tumbler at the lower extremity of said ladder, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, at least one block-and-tackle suspension supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull.
 9. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising a plurality of sections pivoted together for relative swinging movement in a vertical plane only and including an upper tumbler at the top of the ladder, an upper swingable ladder section having a main pivot adjacent its upper end supported by said superstructure, and a lower swingable ladder section pivoted to the section above it and having a lower tumbler at its lower extremity, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, winch means for said cable supported by said hull, sounding means for determining instantaneously the height of the hull above the bottom of the water on which the hull is floating, depth signal means actuated by said sounding means, angle sensing means for determining, instantaneously the angle which the true horizontal makes with the nominally horizontal center line of said hull, angle signal means actuated by said angle sensing means, and control means receiving said depth signal and said angle signal means and controlling the suspension length of at least said lower ladder section and accommodating it to swells in the water level on which the hull floats.
 10. The dredge of claim 9 having a headline extending from shore or sea bottom to said dredge, a headline winch for varying the length of said headline, and a control circuit actuated by said control means for controlling the instantaneous length of said headline during swells.
 11. A floating deep-digging dredge, including in combination, a hull, superstructure supported on said hull, an articulated ladder comprising a plurality of sections pivoted together for relative swinging movement in a vertical plane only and including an upper tumbler at the top of the ladder, an upper swingable ladder section having a main pivot adjacent its upper end supported by said superstructure, and a lower swingable ladder section pivoted to the section above it and having a lower tumbler at its lower extremity, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, winch means for said cable supported by said hull, sounding means for indicating instantaneously the height of the hull above the bottom of the water on which the hull is floating, a first command potentiometer actuated by said sounding means, angle sensing means for indicating instantaneously the angle which the true horizontal makes with the nominally horizontal center line of said hull, a second command potentiometer actuated by said angle sensing means, said winch means comprising a separate luffline winch for each said suspension, a headline extending from shore or sea bottom to said dredge, a headline winch for varying the length of said headline, a third command potentiometer for setting a nominal position of said headline winch, additional command potentiometers, one for setting a nominal position for each said luffline winch, and control means connected to all of said command potentiometers and transmitting the settings of said third and additional command potentiometers to their said winches by a series of outputs, said control means having means for superimposing on said outputs the effects of said first and second command potentiometers, so that the nominal positions of said headline winch and said luffline winches are kept changing to actual positions varying from said nominal positions by amounts such as are needed to keep the position of said lower tumbler substantially constant.
 12. The dredge of claim 11 wherein some of the lufflines have associated with them respective hydraulic cylinders and pistons, said pistons being connected to a translatable sheave, said control means also determining both a nominal position and actual positions for said piston, as determined by the superposition of the command signals.
 13. The dredge of claim 12 having a feedback potentiometer for each winch and each hydraulic piston to provide a base signal at the nominal position thereof, said control means correcting said base signal by an error signal obtained from said first and second command potentiometers.
 14. A floating deep-digging dredge having a hull and a superstructure with a ladder pivotally supported by said superstructure and a digging bucket line passing around an upper driving tumbler supported by the superstructure with the upper pivot for the ladder separately supported by the superstructure and a lower tumbler on the lower end of the ladder and supported by said ladder, characterized by the ladder comprising a plurality of articulated sections pivoted together for relative swinging movement in a vertical plane only, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, and winch means for said cable supported by said hull, the lower end of at least the lowermost ladder section being suspended by two sets of block-and-tackle suspensions lying in the same plane but inclined to each other set at acute angles symmetrical about the center line of the dredge and of the multiple section ladder.
 15. A floating deep-digging dredge having a hull and a superstructure with a ladder pivotally supported by said superstructure and a digging bucket line passing around an upper tumbler-coaxial with the pivot for the ladder and a lower tumbler on the lower end of the ladder and on both sides of said ladder and supported by said ladder, characterized by the ladder comprising a plurality of articulated sections pivoted together for relative swinging movement in a vertical plane only, a plurality of block-and-tackle suspensions supported by said superstructure, each suspension being connected to the lower end of a swingable ladder section for support thereof and having a cable, winch means for said cable supported by said hull, sounding means for determining instantaneously the height of the hull above the bottom of the water on which the hull is floating, depth sigNal means actuated by said sounding means, angle sensing means for determining, instantaneously the angle which the true horizontal makes with the nominally horizontal center line of the hull, angle signal means actuated by said angle sensing means, and control means receiving said depth signal and said angle signal means and controlling the suspension length of at least said lower ladder section and accommodating it to swells in the water level on which the hull floats.
 16. The dredge of claim 15 having a headline extending from shore or sea bottom to said dredge, a headline winch for varying the length of said headline, and means actuated by said control means for controlling the instantaneous length of said headline during swells.
 17. A floating deep-digging dredge having a hull and superstructure supported thereon, including in combination an articulated ladder comprising a fixed uppermost section supported by said superstructure and at least one lower section pivotally supported by said superstructure below and independent from the lower end of said fixed section and in alignment therewith, for relative swinging movement in a vertical plane only, an upper tumbler supported by said superstructure at the top of the ladder, a lower tumbler at the lower extremity of said ladder supported by a said lower section, a digging bucket line passing around both said upper and lower tumbler and on both sides of said ladder and supported by said ladder, block-and-tackle suspension means supported by said superstructure and connected to the lower end of each said lower section for support thereof and having a cable, and winch means for each said cable, supported by said hull.
 18. The dredge of claim 17 in which there is a single swingable ladder section, carrying said lower tumbler.
 19. The dredge of claim 17 wherein there are two swingable lower ladder sections pivoted to each other, the upper of these lower ladder sections being pivoted at its upper end to said superstructure.
 20. The dredge of claim 17 wherein there are at least three swingable lower ladder sections successively pivoted to each other as well as being pivoted to said superstructure at the upper end of the upper section thereof.
 21. A floating deep-digging dredge, including in combination with a hull and a superstructure supported thereon: a fixed uppermost ladder section supported by said superstructure, a swingable ladder portion pivoted at its upper end to said superstructure for relative swinging movement of said swingable ladder portion relative to said fixed ladder section in a vertical plane only, said pivot being supported independently of said fixed ladder section and offset from its axis, said swingable ladder portion comprising at least one ladder section and having an upper tumbler supported by said superstructure co-axial with the pivot of the swingable ladder portion and having a lower tumbler at its lower end, a continuous digging bucket line passing around both said upper and lower tumbler and on both sides of said swingable ladder portions and supported thereby, block-and-tackle suspension means supported by said superstructure and connected to the lower end of each section of said swingable ladder portion for support thereof, each unit thereof having a cable, winch means for said cable supported by said hull, a continuous transfer and delivery bucket line supported by said fixed uppermost ladder section, to which said digging bucket line transfers its load as it passes over said upper tumbler, and means for receiving the load from said transfer and delivery bucket line as it passes over the top of said fixed uppermost ladder section, at a constant angle.
 22. The dredge of claim 21 wherein said means for receiving includes inclined grizzly bars and a secondary receiving chute.
 23. The dredge of claim 21 wherein said swingable ladder portion comprises two sections pivoted to each other, the upper ladder section being the one pivoted at its upper end to said superstructure.
 24. The dredge of claim 21 wherein said swingable ladder portion comprises three sections successively pivoted to each other as well as being pivoted to said superstructure at the upper end of the upper section thereof.
 25. A floating deep-digging dredge having a hull and a superstructure with a ladder pivotally supported for relative swinging movement in a vertical plane only, by said hull and excavating means on the lower end of the ladder, characterized by block-and-tackle suspension means for the ladder supported by said superstructure and connected to the lower end of at least one swingable ladder section for support thereof and having a cable, winch means for said cable supported by said hull, sounding means for determining instantaneously the height of the hull above the bottom of the water on which the hull is floating, depth signal means actuated by said sounding means, angle sensing means for determining, instantaneously the angle which the true horizontal makes with the nominally horizontal center line of said hull, angle signal means actuated by said angle sensing means, control means receiving said depth signal and said angle signal means and controlling the suspension lengths of said ladder and accommodating it to swells in the water level on which the hull floats.
 26. The dredge of claim 25 having a headline extending from shore or sea bottom to said dredge, a headline winch for varying the length of said headline, and a control circuit actuated by said control means for controlling the instantaneous length of said headline during swells.
 27. The dredge of claim 25 wherein said depth signal means comprises a first command potentiometer actuated by said sounding means, and said angle signal means comprises a second command potentiometer actuated by said angle sensing means, said winch means comprising a separate luffline winch for each said suspension, a headline extending from shore or sea bottom to said dredge, a headline winch for varying the length of said headline, a third command potentiometer for setting a nominal position of said headline winch, additional command potentiometers, one for setting a nominal position for each said luffline winch, control means connected to all of said command potentiometers and transmitting the settings of said third and additional command potentiometers to their said winches by a series of outputs, said control means having means for superimposing on said outputs the effects of said first and second command potentiometers, so that the nominal positions of said headline winch and said luffline winches are kept changing to actual positions varying from said nominal positions by amounts such as are needed to keep the position of said excavating means substantially constant.
 28. The dredge of claim 27 wherein some of the lufflines have associated with them respective hydraulic cylinders and pistons, said pistons being connected to a translatable sheave, said control means also determining both a nominal position and actual positions for said piston, as determined by the superposition of the command signals.
 29. The dredge of claim 28 having a feedback potentiometer for each winch and each hydraulic piston to provide a base signal at the nominal position thereof, said control means correcting said base signal by an error signal obtained from said first and second command potentiometers.
 30. A floating deep-digging dredge having a hull and a superstructure with a ladder pivotally supported for relative swinging movement in a vertical plane only, by said hull and excavating means on the lower end of the ladder, characterized by the ladder comprising a plurality of articulated sections pivoted together for swinging movement in said vertical plane, block-and-tackle suspension means for the ladder supported by saiD superstructure and connected to the lower end of at least one swingable ladder section for support thereof and having a cable, winch means for said cable supported by said hull, means supported by said hull independently of said excavating means and connected to said winch means for rotation of said winch means for controlling the suspension lengths of said ladder, and means supported by said hull for moving said hull horizontally fore and aft in synchronization with said means for controlling the suspension lengths of said ladder, for accommodating said ladder vertically and horizontally to swells in the water level on which the hull floats to keep the position of said excavating means relative to the sea bottom and dredging face substantially constant. 